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TEST QUESTIONS & PROBLEMS – CHAPTER #7
Short Answer Questions
1. (T or F) Aquifer permeability is affected by groundwater temperature.
2. Why is the velocity head component of hydraulic head not considered in Darcy’s equation?
3. The three different types of groundwater velocity include all of the following except:
a) pore velocity b) apparent velocity c) actual velocity d) seepage velocity
4. (T or F) The higher the porosity, the easier it is to extract water from an aquifer.
5. Name the three different types of groundwater velocity and define each.
6. (T or F) The theoretical upper limit of porosity is 100%.
7. Explain the difference between a confined and an unconfined aquifer.
8. Withdrawals from aquifers can result from which of the following mechanisms?
a) springs b) wells c) influent streams d) infiltration of rainwater e) transpiration
9. Define two limitations to laboratory determined permeabilities using core samples.
10. The ratio of volume of voids to total volume in porous media is called:
a) void ratio b) specific yield c) water ratio d) porosity
11. (T or F) In general, the porosity of gravel is higher than that of clay.
12. What is the difference between seepage velocity and actual velocity?
13. Show all steps in the proof of the well equation for unconfined aquifer under state flow
conditions starting with Darcy’s expression: Q = 2πrhK(dh/dr).
14. (T or F) A homogeneous aquifer implies the permeability is independent of flow direction.
15. Define the cone of depression in groundwater flow.
16. When the permeability of an aquifer is dependent upon direction, the appropriate term is:
a) homogeneous b) heterogeneous c) isotropic d) anisotropic e) don’t know
17. Describe how you would determine the drawdown in a confined aquifer at a location that was
impacted by two pumped wells in the vicinity. What principle is being invoked?
18. A 50 cm3 sand sample is collected from an aquifer. When the sample is oven dried and
poured into a graduated cylinder, it displaces 30 ml of water. Determine the porosity.
19. (T or F) In confined aquifers, the value of the storage coefficient is much lower than in
unconfined aquifers.
20. Why is the storage coefficient larger in confined aquifers than in unconfined aquifers?
21. Which of the following terms is a dimensionless number defined as the water yield from a
column of aquifer (of unit area) that results from lowering the water table or piezometric
surface by a unit height.
a) porosity b) permeability c) hydraulic conductivity d) transmissibility e) storage coefficient
22. Describe the difference between steady and unsteady radial flow in an unconfined aquifer.
23. (T or F) For unsteady radial flow in confined aquifers, the principal of superposition may be
used to solve for the drawdown of multiple wells and for unsteady well pumping rates.
24. For unsteady radial flow in confined aquifers, which of the following parameters affect the
drawdown at a specific location within the radius of influence?
a) time since pumping began b) the radial distance from the well to the point of interest
c) transmissibility d) storage coefficient e) the well pumping rate
25. Define the term aquifer recovery in unconfined aquifers.
Ans. Aquifer recovery is the rise of the water table once pumping of the well has stopped.
26. (T or F) The basic idea (premise) in analyzing field pumping test data to determine an aquifer’s
hydraulic characteristics is to fit the observed drawdowns to available analytical solutions.
27. Why are field pumping tests more reliable in determining an aquifer’s hydraulic paramenters
than laboratory tests done on aquifer samples.
28. (T or F) An aquifer’s storage coefficient can be obtained from a field pumping test under
equilibrium (steady aquifer flow) conditions.
29. All of the following items are required for an equilibrium test in a confined aquifer except:
a) the aquifer storage coefficient b) drawdown measurements in at least two wells
c) drawdown measurements taken after aquifer equilibrium is achieved
d) radial distances to the wells where drawdowns are being measured
30. All of the following are required for an equilibrium test in an unconfined aquifer except:
a) a completely penetrating pumped well b) pump flow equilibrium must be achieved
c) drawdown measurements in at least two wells d) radial distances to the observed wells
31. (T or F) Analytical solutions are not available for unsteady flow in unconfined aquifers to
determine the storage coefficient.
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32. Identify two different types of aquifer boundaries that will upset the radially-symmetric
drawdown pattern of a pumping well if the boundary is within the radius of influence.
33. In order to use the method of images to solve aquifer boundary problems, which of the
following limitations must be met:
a) the aquifer must be confined b) the aquifer must be unconfined
c) the boundary must fully penetrate the aquifer d) the aquifer flow must be steady
34. (T or F) An impermeable boundary next to a well will increase the drawdown between the
boundary and the well when compared to radially-symmetric drawdown conditions.
35. Define an image well.
Ans. Hydraulic image wells are imaginary sources or sinks, with the same strength (i.e., flow
36. (T or F) Drawdowns for unconfined wells are linear; thus the drawdown of a well and its
image can be added to obtain the drawdown created when a well operates near a boundary.
37. Draw the system of images to replace
the boundary conditions depicted
(recharge/river & barrier/impermeable).
Show all distances, and whether the
image well is a discharge well or a
recharge well.
38. Which of the following methods are not used to determine the presence of groundwater?
a) electrical resistivity b) fluid capacitance c) hydraulic spectrophotometry
d) seismic wave propagation e) infrared telemetry f) devination
39. (T or F) The process of saltwater penetrating freshwater aquifers near the coast is called sea
water intrusion.
40. Sketch the saltwater-freshwater interface of an unconfined coastal aquifer.
Ans.
41. Define equipotential lines.
42. Flow nets drawn under a dam allow you to determine all of the following except:
a) the amount of seepage b) the hydrostatic pressure anywhere in the net
c) the seepage velocity anywhere in the net d) the porosity anywhere in the net
43. Identify two methods used to control sea water intrusion.
44. (T or F) Divination is an ancient art used to locate groundwater.
45. Excessive seepage through an earth dam could lead to which of the following:
a) piping b) cavitation c) scaling d) sloughing e) global warming
46. Define piping.
47. (T or F) The upper surface of the seepage flow through an earth dam is known as the surface
of saturation or phreatic surface.
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Problems
1. A permeameter experiment is being set up to determine the permeability of some very fine
sands. The cylindrical test samples used are 30 cm long and have a diameter of 10 cm. Also,
50 ml of water will be collected using a head difference of 40 cm. Estimate how much time
each experiment will take in minutes? Also, estimate how much time (on average in hours)
will it take a conservative tracer to pass through the test sample?
2. A high-water table exists behind a retaining wall shown in the figure below. Weep holes are
drilled at the bottom of the retaining wall every 3.0 m to alleviate the hydrostatic pressure. If
the permeability is 10–5 m/s, determine the seepage (in cm3/sec) through each weep hole.
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3. A chemical spill occurs at a manufacturing plant. Sampling reveals the conservative pollutant
is now in the groundwater directly under the location of the spill. If the aquifer is composed
of sand and gravel, how many hours will it take the pollutant to travel 82 feet to the property
boundary assuming the aquifer is homogeneous and the water table has a slope of 2%.
4. A fully penetrating well in a 33 m thick confined aquifer pumps at a constant rate of 2000
m3/day for a long time. In two observation wells located 20 m and 160 m from the well, the
difference in hydraulic head is 2.0 m. If the undisturbed head is 250 m, and the head in the
furthest observation well is 249 m, calculate the radius of influence of the well.
5. After pumping a 12-in.-diameter well for a long time, equilibrium conditions have been